Once the egg yolk mix has doubled in size and turned pale in colour, remove the bowl from the heat and whisk in the melted butter until a thick sauce is formed, one that coats the back of a spoon and hangs. Adjust the seasoning with salt and lemon juice before serving.
The first sister sauce is béarnaise, which requires the addition of tarragon, chives and shallots - perfect with roasted meats.
Paloise sauce requires the addition of finely chopped mint; and choron sauce calls for the addition of tomato paste, which makes it a perfect addition for shellfish.
Another delicious derivative is mousseline sauce, where the addition of lightly whipped cream creates the perfect sauce for either steamed fish or poultry.
The last one is slightly more advanced. It's basically a fancy version of hollandaise. Take the original hollandaise and add 100 ml of low-fat milk. Adjust the seasoning with some lemon juice and salt. Then pour it straight into a siphon gun.